I have a 110 year old house and the underside of the first floor is not insulated, so the only thing between my crawl space and living area is the original pine floor. First of all, how bad of a situation is this in terms of energy loss? Assuming it needs to be addressed, about 70% of the house is over a crawl space that is barely accessible. It takes a pretty small person to get in there, and it's still an army crawl to move around. I've begun digging it out from the cellar, but, aside from the amount of digging, there are gas pipes and HVAC ducts in the way. I should also note that the perimeter of the cellar (brick foundation) is not insulated and does have leaks. I feel like I've got a bad situation here, so what are my best options? I would guess that ideally, it would be dug out with modifications to the HVAC where needed; liner put down; and insulation installed. Short of that, is there anything I can do that would be second best?

I'd plug the leaks in the walls of the crawlspace, put down plastic sheeting over the dirt to reduce water vapor and make it nicer to crawl on. Then I'd insulate the walls of the crawlspace. Should make a big difference in comfort and mustiness.

What type of insulation should be used? I'd like to lay down plastic, but I think I'd have to dig out under the HVAC ducts and gas pipe that runs from the front of the house to the back of the house. I think to do anything right, I'm looking at a lot of difficult digging (and hauling). ugh. I can't understand why a crawlspace would be made too small for an average person to crawl in.